When manufacturing a semiconductor device, a process of forming an opening (via hole) has been used in many cases. As disclosed in JP 2007-311584A and JP 2009-044031A, a Bosch process has been known as a means for forming a deep opening having a vertical shape in a semiconductor substrate such as silicon. The Bosch process is a technology that repeats an etching process of isotropically etching a surface of the semiconductor substrate to form an opening and a deposition process of depositing a carbon polymer-based protective film on an inner wall of the opening alternately, thereby etching the semiconductor substrate vertically and deeply.
FIG. 23 is a sectional view of an opening 31 that is formed in a semiconductor substrate 30 by the Bosch process according to the related art. In the Bosch process, since the etching process and the deposition process are repeated, it is known that a sectional shape of a waveform referred to as scalloping (which is indicated with ‘S’) is formed on side surface of the opening 31.
FIG. 24 shows an opening forming method using the Bosch process according to the related art. A mask 32 having an opening pattern is formed on the semiconductor substrate 30 with a photoresist film and the like (not shown).
As shown in FIG. 24A, in a first cycle, a first opening 31-1 is formed by dry etching having high isotropy and using etching gas (first etching process).
As shown in FIG. 24B, a protective film 33 that covers an inner wall of the first opening 31-1 and a top surface of the mask 32 is deposited by using deposition gas (deposition process).
As shown in FIG. 24C, the dry etching in which the anisotropy is increased by using the etching gas is performed to remove the protective film 33 on a bottom of the first opening 31-1 (second etching process). The protective film 33a remains on side surface of the first opening 31-1.
As shown in FIG. 24D, in a second cycle, a second opening 31-2 is formed by the isotropic dry etching (first etching process). When performing the etching, a part of the protective film 33a is also removed.
By repeating the series of cycles more than once (for example, 200 times), the opening 31 having the substantially vertical shape and a predetermined depth as shown in FIG. 23 is formed.